Note: Descriptions are shown in the official language in which they were submitted.
CA 02357367 2001-09-13
METHOD FOR PRODUCING METHYLENE UREA POLYMERS
The present invention relates to a method for producing methylene urea
polymers using at least
urea, a formaldehyde product and an acid.
In the production of fertilizers urea is of particular importance, since it
contains a high proportion
of nitrogen and can be produced at low cost. However, it is rather
uneconomical to use pure
urea as fertilizer because pure urea washes out easily and is highly volatile.
It is known to employ urea in a compound with formaldehyde as fertilizer. In
this compound,
which is also referred to as methylene urea, the above described negative
properties of urea are
avoided to a large extent.
A method as described above for producing methylene urea is disclosed in for
example DE-PS
24 22 238. According to one embodiment free urea is first adjusted with a
mineral acid to a
particular pH-value in a stirrer vessel. In a next step a pre-condensate
consisting of urea and
formaldehyde is added while a particular temperature has to be kept over a
longer period of
time. After completing the reactions for the production of the intended
product condensate this
condensate is approximately neutralized in a subsequent method step by adding
alkali. In an
additional step a filtration is then carried out. While the filtrate is lead
into the reaction vessel
again the moist condensate is dried and processed to the desired end product.
This known method requires great expenditure regarding both the apparatus
needed and the
2 5 time involved.
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CA 02357367 2001-09-13
An object of the present invention is to provide a method for producing
methylene urea, which
can be carried out in a quick as well as simple and therefore cost-effective
manner.
According to the present invention there is provided a method for producing
methylene urea
polymers from urea, a formaldehyde product and an acid, which comprises the
steps of
introducing urea with the formaldehyde product into a first section of a multi-
screw extruder,
mixing the urea in the first section of the extruder with the formaldehyde
product, compressing,
heating and thereby melting to a flowable mixture, in a subsequent section of
the extruder adding
the acid to the flowable mixture and mixing with the flowable mixture,
reacting the flowable
l0 mixture with the acid by forming a mass having methylene urea polymers, and
extruding the
mass.
In this way the entire method can be carried out in a continuous fashion in a
single device.
Moreover, since the process area is enclosed by the extruder housing, an
undesired escape of
reaction intermediates, ammoniak for example, is avoided to a large extent.
For the production
of methylene urea the individual reaction products are fed into the extruder
at a high dosing
precision. The mixing of urea with the formaldehyde product in the multi-screw
extruder leads,
upon interaction with the compression and the simultaneous heating, to a very
homogenous melt.
This is in turn an essential precondition because when the acid is also fed at
a high dosing
2 0 precision and when being thoroughly mixed a quick and near complete
reaction of the starting
products leads to the desired methylene urea polymers. The use of a multi-
screw extruder
having at least two screws, which can be driven synchronously or in counter-
rotation, is of
particular importance here. For it is only the interaction of meshing extruder
screws that leads
to a large reaction surface between the starting products. This is a
precondition for a near
2 5 complete reaction.
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CA 02357367 2001-09-13
As a result of the precise dosage of the starting products in a continuous
process and due to
significant latitude in choosing the reaction parameters with regard to
mixing, temperature,
compression, reaction times, etc. it is rendered possible for the first time
with the method
according to the present invention to adjust at high precision the result of
the reaction with
respect to the chain length of the produced polymers. Thus, methylene urea can
be produced
as desired with a high proportion of short-chain methylene urea polymers, such
as
methylenediurea or dimethylenetriurea, or with a high proportion of long-chain
polymers, such
as trimethylenetetraurea, tetramethylenepentaurea etc.
1 o Compared to the prior art known so far, the method according to the
present invention therefore
not only offers advantages with respect to a compact, low-cost device as well
as a quick
performance of the method but also with respect to the production of a
plurality of precisely
defined end products.
For the purpose of performing the method in a particularly effective way it
has proved to be
advantageous that paraformaldehyde be used as the formaldehyde product.
A further increase in efficiency of the method performance is achieved
according to the present
invention when hexamethylenetetramine and/or tetramethylenediamine is
introduced into the
2 0 extruder together with urea and the formaldehyde product and melted to the
mixture. With this
an altogether dehydrated process can be achieved such that a drying process
can be dispensed
with or can at least be drastically reduced.
For the final reaction to produce methylene urea almost any common acid can be
employed.
With regard to the costs and the reaction safety it is of advantage to use as
acid phosphoric,
hydrochloric and/or sulphuric acid.
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CA 02357367 2001-09-13
In principle the melting of the mixture in the first extruder section can be
effected merely by the
frictional heat that develops as a result of the transport and the compression
of the reaction
products. However, for a gentle and at the same time quick heating it is
possible according to
an embodiment of the present invention that the heating of the mixture in the
first extruder
section is effected by using heating elements on the extruder. The heating
elements can be
electric heating coils or heating water pipes disposed inside or on the
extruder housing along
a particular heating section. In this way any desired heating temperature as
well as a purpose-
directed temperature control can be adjusted in a simple way. For the melting
of the mixture the
preferred temperature range lies between 60°C and 120°C.
However, higher or lower
to temperatures can also be chosen for particular method variants.
In a particularly preferred embodiment of the method according to the present
invention an
active substance, such as another fertilizer, a plant protective, a growth
regulator etc. is
additionally introduced into the extruder and incorporated into the mass
consisting of methylene
urea polymers. It is useful to feed the supplementary active substance after
feeding the acid
and after the reaction to methylene urea has been largely completed. With the
active substance
used together with methylene urea a combined fertilizer or another combined
preparation can
thus be produced in the same method step and in the same device. Particularly
in the very
price-sensitive market segment of fertilizers this leads to definite economic
advantages.
Since the mixture of substances and the mass are still in a melted state the
additional active
substances can be introduced at the precise dosage through a so-called side
feeder or another
suitable feeding device and processed in the extruder to a homogenous mass. In
this way a
complex combination fertilizer or preparation can be produced without any
intermediate product
and the transportation and storage processes that are otherwise involved
therewith.
Furthermore, the feeding of the additional active substances into the still
liquid or flowable mass
of methylene urea polymers has the further advantage that the additional
active substances can
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. CA 02357367 2001-09-13
be incorporated without any binding agent. Consequently, a fertilizer can be
produced on the
basis of methylene urea with additional active substances, which fertilizer
can be absorbed by
the plants without leaving any residues in an ecologically and economically
appropriate manner.
When feeding nitrogen, phosphorus and/or kali fertilizer salts it is preferred
in certain cases to
additionally inject water into the extruder together with the active substance
in order to ensure
a good dissolution of the nutrient salts and a good mixing and blending with
methylene urea.
According to the present invention it is also preferred to lead the mass
through a forming tool
and/or a granulating tool after exiting the extruder. In doing so the end
product can be adjusted
1o as to size and shape immediately upon the exit of the mass from the
extruder. Afterwards a
short drying period and, if needed, a rounding of the granulated material is
required.
As far as the drying is concerned it is preferred that the mass is dried by
means of a drying
device following the exit from the extruder. This can be a rotary furnace a
conveyer belt which
runs along heating elements, or the like.
According to another preferred embodiment of the method according to the
present invention
the proportions of the methylene urea polymers having a different chain length
are adjusted
relative to each other in a defined manner by controlling the feeding of the
individual substances
2 o into the extruder. The control can be directed at both a quantitative and
a qualitative change of
the feeding components. As feeding devices side feeder pumps, dosing pumps
etc., driven by
controllable electromotors, or controllable valves can be provided on feeding
vessels or feeding
lines. The feedings can be controlled entirely by a controlling computer such
that desired
product changes or product variants can be adjusted from a central station in
a simple and quick
2 5 way.
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CA 02357367 2001-09-13
Instead of using an acid, a different substance with an acid reaction, such as
an acid salt, can
also be employed. For example ammonium sulphate which is a good donor of H+
ions can be
employed.
Where the quantitative composition is concerned the method can be carried out,
with respect
to 100 weight percent of methylene urea produced, using 50%-90% urea, 5%-40%
formaldehyde product, 0%-10% hexamethylenetetramine as well as a remainder of
acid. By
deliberately changing the proportions, the chain length of the polymers and
their proportions
relative to each other can be adjusted which can be easily established by
tests.
l0
In the following a detailed description of the invention is given with
reference to a preferred
embodiment, a schematic of which is shown in the single Figure.
This single Figure illustrates schematically an arrangement of a device for
performing an
embodiment of the method according to the present invention.
This device comprises a multi-screw extruder 7 which is preferably driven in
counter-rotation.
In a first vessel 1 there is urea which is lead to a weighing belt 5 together
with paraformaldehyde
from another vessel 2 as well as hexamethylenetetramine from yet another
vessel 3. The
weighing belt 5 serves as a dosing device to compose the aforementioned
starting products in
a precise quantitative way.
The aforementioned starting products are introduced over the weighing belt 5
into an inlet of the
extruder 7. In a first section A of the extruder 7 urea, paraformaldehyde and
hexamethylenetetramine are mixed with each other, compressed and melted as a
result of the
frictional heat present in the extruder 7 and due to a heating capacity of
heating elements that
are not depicted. The melting temperature of the mixture lies between
60° and 90°C.
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CA 02357367 2001-09-13
The mixture melted in this way is lead in the course of the extruder 7 to
another section K of the
extruder 7 in which phosphoric acid is added to the melted mixture from an
acid vessel 4. The
liquid acid is injected into the extruder 7 through an injection device, which
is not illustrated in
detail, such that in combination with the mixing effect of the two extruder
screws, a good mixing
of the reaction products and thus a high reaction surface is achieved. In this
way a quick and
practically complete condensation to methylene urea can take place. After the
reaction zone
inside the extruder 7 the mass is cooled down and, upon reaching a particular
solidity, is
extruded at the exit of the extruder 7 through a forming tool 6.
to Depending on the consistency of the produced mass and the desired end
product a granulating
device may be provided on the forming tool 6, which device cuts the extruded
strands to a
desired length. The extruded material is lead over a belt-shaped drying device
T where it is
dried to a desired degree. Following the drying step the end product can in
addition be rounded
for particular applications or directly filled and thus be prepared for
dispatch.
In a preferred performance of the method the mass is composed of 80% urea, 13%
paraformaldehyde, 3% hexamethylenetetramine as well as 4% phosphoric acid.
From the explanation set out above it becomes apparent that a particularly
simple, cost-effective
2 0 and yet still very precise method for producing methylene urea is provided
by the method
according to the present invention.
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